1. Field of the Invention
The present invention relates to controllers for voltage controlled oscillators and, more particularly, to noise generators that control voltage controlled oscillators as used in radar jammers.
2. Description of the Prior Art
In the practice of the radar art, it is common to limit the detection capabilities of a radar set by deliberately generating external noise of a relatively high power level in comparison to normal receiver noise and directing this generated noise signal at the radar set. Devices for generating such noise signals and transmitting them toward the target radar are commonly known in the radar art as jammers. In radar jammer systems of the prior art, the jamming signal was transmitted in response to a center frequency input signal, noise quality input signals, and noise modulation input signals. Basically, a jammer is comprised of three subsystems: a waveshaping network for providing noise quality and noise modulation signals; a noise generator that generates a noise output signal, the spectrum of the noise output signal being controlled in response to the noise quality and noise modulation signals of the waveshaping network; and a voltage controlled oscillator that transmits a jamming signal in response to the noise output signal.
The random noise signal was usually generated from a source within the noise generator and controlled by the input signals of the waveforming network to generate a noise signal spectrum having predetermined nominal frequency, quality and modulation. In the prior art, the spectrum of the noise generator output signal was controlled in response to a center frequency control signal that determined the center of the spectrum range, noise quality input signals that determined the quality and range of the spectrum, and noise modulation input signals that controlled the modulation of the spectrum. As generally known in the art, the center frequency input signal which determined the nominal location of the generated noise signal spectrum, was a substantially constant level signal and afforded a potential for tuning the noise spectrum to a particular nominal value by adjusting the level of the center frequency input signal. The noise quality input signals which controlled the quality or type of generated noise signal included the random noise signal itself and a control signal of some predetermined function as, for example, a ramp function control signal. The control signal such as the ramp signal was provided to obscure the definition of discrete values in the generated noise signal spectrum. The noise quality input signals also included control signal bandwidth and noise bandwidth input signals that determined the range of the generated noise signal spectrum. The noise modulation input signals that controlled the modulation of the noise signal spectrum included wobbulated waveform and wobbulated bandwidth input signals. As the use of the term "wobbulated" suggests, these input signals were periodic signals of some predetermined shape in which the period of the signal was modulated in a periodic manner.
However, in previous jamming systems, the center frequency noise quality and noise modulation input signals provided to the noise generator were combined with the random noise signal in analog form. Where the input signals provided to the noise generator were in digital form, these signals were converted to analog form prior to their combination with the other input signals and the random noise signal. For many applications of such prior art jammers, the relatively slow response times of currently available amplifiers required the use of several parallel signal channels which were then multiplied together and provided to a single driver circuit to generate a noise spectrum in the required time. To simultaneously provide a plurality of noise spectrums the driver circuit was multiplexed between a plurality of multiples, each of which generated the noise spectrum. The stringent switching speed requirements for the multiplexer and driver circuit to simultaneously provide a plurality of noise signal spectrums became difficult to attain. Furthermore, due to the relatively large number of components required for the construction of the parallel channels, MHP or other high density packaging technology was frequently used in applications where the physical size of the jammer was a limiting factor. However, such high density packaging technology made the jammers relatively expensive and significantly increased the time required for their construction.
Therefore, there was a need in the prior art for a noise generator that was better adapted for operating at the relatively high speeds required to simultaneously generate a plurality of noise spectrums and which would not incur the expense and production difficulties commonly experienced with high density packaging technology.